1. Field of the Invention
The present invention relates to a paper floating detection apparatus, a paper conveyance apparatus and an image recording apparatus, and more particularly to a paper floating detection apparatus, a paper conveyance apparatus and an image recording apparatus for detecting floating of paper in an inkjet recording unit of an inkjet recording apparatus, by means of detection light.
2. Description of the Related Art
A known image forming apparatus is an inkjet recording apparatus (inkjet printer), which has an inkjet head in which a plurality of nozzles (ink ejection ports) are arranged, and which forms an image on a recording medium by conveying the recording medium relatively with respect to the inkjet head and ejecting droplets of ink toward the recording medium from nozzles.
In the inkjet recording apparatus, when the inkjet head and the recording medium are conveyed relatively to each other, since the nozzles of the inkjet head are situated in very close proximity to the conveyed recording medium, then if the recording medium floats up from the conveyance surface while passing in the vicinity of the inkjet head, then image quality deteriorates due to change in the height at which the ink droplets are ejected, the nozzle surface may be damaged by the recording medium rubbing against the nozzle surface, or the recording medium may strike against the nozzles and cause dirt to become attached to the recording medium, and furthermore, there may be problems such as ejection failure due to paper dust blocking up the nozzles.
Therefore, various detection apparatuses have been proposed in the related art in which a light-emitting element and a light-receiving element are arranged in mutual opposition in such a manner that detection light emitted from the light-emitting element is received by the light-receiving element, and the floating of the recording medium and the ejection state of the ink droplets are determined by detecting either the recording medium or ink droplets passing through the detection light.
For example, Japanese Patent Application Publication No. 2007-076109 discloses a droplet ejection apparatus which includes a light-emitting element arranged on one side of a direction perpendicular to a direction of conveyance of a droplet ejection head, and a light-receiving sensor arranged on the other side, and a detection device which optically determines the height from a recording medium conveyance device by passing a light ray between a conveyance device which holds a recording medium and conveys the recording medium so as to face a droplet ejection head, and the droplet ejection head, the light ray being passed at a height above the conveyance device.
Moreover, for example, Japanese Patent Application Publication No. 2002-172805 discloses an inkjet recording apparatus in which an ink collection unit which collects ink droplets inside an ink droplet ejection region, a suction fan for forming an air flow toward an ink suction port connected to the ink droplet ejection region provided in the ink collection unit, and a plurality of ink shielding walls having light transmission ports for transmitting light projected from a light emission module to a light reception module are arranged in respect of an ink droplet ejection region which is interposed between a light emission module and a light reception module that determine the ejection state of ink droplets from a nozzle forming surface of an inkjet recording head; ink droplets ejected from the nozzle forming surface onto the ink droplet ejection region become an ink mist and are borne on the air current toward the ink suction port and collected by the ink collection unit, thereby preventing soiling of the light emission module and the light reception module by the ink mist and thus preventing decline in the detection accuracy of the ink ejection state.
Furthermore, for example, Japanese Patent Application Publication No. 09-226150 discloses an inkjet recording apparatus which includes an ink end detection device which records marks by ejecting ink onto a recording paper, and detects that ink has run out by detecting the presence or absence of the marks, an obstructing wall member which prevents external light from entering into the ink end detection apparatus that detects the presence or absence of marks is provided in a recording paper output tray, so as to prevent mistaken detection that ink has run out.
However, in the technology described in Japanese Patent Application Publication No. 2007-076109, the environment of the optical path between the light-emitting element and the light-receiving element is not kept uniform by covering the optical path. Moreover, in the technology described in Japanese Patent Application Publication No. 2002-172805, the whole of the optical path formed by the light emission module and the light reception module is not covered by a cover, and the described air flow is not intended to uniformize the temperature. Furthermore, the obstructing wall members described in Japanese Patent Application Publication No. 09-226150 do not prevent temperature change.
In the above-described technology in the related art, no consideration is given to change in the amount of received light due to bending of the optical path of the detection light, which is affected by changes in the air flow and temperature in the periphery of the detection light path, and hence there is a concern that erroneous detection may occur as a result of ambient changes, such as change in the air flow or temperature in the periphery of the detection light path.
Furthermore, although it might be possible to provide dividing plates inside the apparatus as a general method of controlling the temperature differential and the direction of the air flow, in a large apparatus, the dividing plates will also be large, and there is a problem in that the number of components increases in order to cover the gaps in the drive units, and therefore the apparatus becomes complex. Moreover, a method for suppressing the flow of air caused by rotation of a drum having undulations to eliminate air flow in the periphery of the optical path, and modifications for preventing temperature change, are not known in the related art.
As described above, in an inkjet recording apparatus, if the floating height of the recording medium is equal to or greater than a prescribed specific value in the recording unit, there is a risk of the recording medium rubbing against the nozzle surface of the head and causing damage to the head, and therefore it is necessary to detect the floating of the recording medium and halt the conveyance of the recording medium accordingly, before the recording medium which has floated up by a specific value or more enters into the recording unit.
In cases where a detection mechanism including a transmissive photoelectric sensor which transmits detection light in a substantially perpendicular direction to the recording medium conveyance direction is disposed in order to detect floating of a recording medium, apertures being provided respectively before the light emission surface and the light reception surface of the sensor and floating of the recording medium being detected when the light between the apertures is shielded by the recording medium, if the ambient change in the periphery of the detection light path is not taken into account as described above, then there is a problem in that the optical path bends due to temperature difference if, for example, air having a different temperature to that of the recording medium or the conveyance surface passes through the optical path of the detection light, and therefore floating of the recording medium cannot be detected at the correct height.